JP2951252B2 - Ultrasound Doppler diagnostic device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic Doppler diagnostic apparatus, and more particularly to a pulse Doppler or continuous wave Doppler ultrasonic Doppler diagnostic apparatus capable of changing the transmission frequency (transmission / reception frequency) of ultrasonic waves.

[0002]

2. Description of the Related Art An ultrasonic Doppler diagnostic apparatus transmits an ultrasonic wave into a living body, receives a reflected wave reflected by a moving reflector (blood flow or the like) in the living body, and thereby receives the moving reflector. A Doppler image representing the exercise information is displayed.

As a Doppler image in the pulse Doppler method, a power spectrum image, a color two-dimensional Doppler image, and the like are known. This power spectrum image is an image in which the horizontal axis is the time axis, the vertical axis is the Doppler shift frequency, that is, the speed, and the power at each Doppler shift frequency corresponds to the magnitude of the luminance, and is set to a specific direction and a specific depth. It is formed by frequency analysis of the received signal from the sample point. The two-dimensional Doppler image is an image in which the Doppler shift frequency, that is, the speed of each point in a two-dimensional region in a living body is represented by a change in hue.

In the above-described power spectrum image and two-dimensional Doppler image, the maximum measurable Doppler shift frequency f _{d max} is defined by １ ／ of the transmission repetition frequency f _{pr in} each of the positive and negative directions. That is, the maximum measurable Doppler shift frequency f
_{d max} is f _{d max} = f _pr / 2 (1) In this regard, in the following known relational expression f _d = (2 v · cos θ · f ₀ ) / c (2), substituting equation (1) for cos θ = 1 and f _d , the maximum speed v that can be analyzed is _max is obtained as follows.

V _max = (c · f _pr ) / (4 · f ₀ ) (3) where f _d is a Doppler shift frequency, f ₀ is a center frequency of an ultrasonic pulse, and c is an ultrasonic pulse. The speed of sound in a living body.

On the other hand, examples of Doppler images in the continuous wave Doppler method include a spectrum display and a waveform display of an average flow velocity on a time axis. In this continuous wave Doppler method, it is known that the maximum measurable Doppler shift frequency f _{d max} is f _{d max} = f _q / 2 (4). Therefore, the maximum speed v _max that can be analyzed is obtained as follows: v _max = (c · f _q ) / (4 · f ₀ ) (5) as in the above equation (3).

Conventionally, in a pulse Doppler system and a continuous wave Doppler system ultrasonic Doppler diagnostic apparatus, unnecessary echoes from a low-speed and strong reflector (for example, a heart wall) in a living body prior to processing by a frequency analysis unit. To remove clutter, a low-pass rejection filter (clutter rejection filter)
Is provided. The conventional low-pass filter is constituted by an analog filter, and its cutoff frequency f _hp is fixedly set. Note that the cutoff frequency f _hp
Speed v _hp, which corresponds to is determined in the following manner.

V _hp = (c · f _hp ) / (2 · f ₀ ) (6)

[0009]

By the way, in an ultrasonic diagnostic apparatus, various ultrasonic probes can be connected in accordance with a part to be diagnosed, and at that time, an ultrasonic wave is transmitted in accordance with each ultrasonic probe. The frequency f ₀ can be variably set. In recent years, there has been proposed an ultrasonic Doppler diagnostic apparatus that allows an operator to freely and variably set an optimal ultrasonic transmission frequency f ₀ while viewing a Doppler image even with the same ultrasonic probe.

However, if the transmission frequency f _{0 of the} ultrasonic wave is varied, the Doppler shift frequency f _d also changes in proportion to the change, as is apparent from the above equation (2). There was a problem that it would change.

That is, when the transmission frequency f ₀ of the ultrasonic pulse is increased, the Doppler shift frequency f _d is increased in proportion, but on the other hand, the speed display range in the Doppler image is reversed as apparent from the above equation (3). Will decrease. Conversely, when the transmission frequency f ₀ of the ultrasonic pulse is reduced, the Doppler shift frequency f _d is reduced in proportion, but on the other hand, the speed display range in the Doppler image is apparent from the above equation (3). It will increase conversely.

As described above, when the transmission frequency f ₀ fluctuates, the Doppler shift frequency f _d and the speed display range in the Doppler image fluctuate in inverse proportion to each other, even though the blood flow velocity is originally constant. In this regard, focusing on the display waveform, since the size of the display area is fixed, an increase or decrease in the transmission frequency f ₀ of the ultrasonic pulse appears as an enlargement or reduction of the waveform. This problem is similarly pointed out when the continuous wave Doppler method is applied.

Further, the above problems have been pointed out with respect to the low-pass Filters, despite the Doppler shift frequency f _d varies, in the conventional device is fixed cutoff frequency, in other words, As is apparent from the above equation (6), when the transmission frequency f ₀ is increased or decreased,
Even if the blood flow velocity does not fluctuate, the velocity corresponding to the cutoff frequency fluctuates in inverse proportion thereto, making it difficult to properly shut off only the target clutter.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to prevent the display content of a Doppler image from changing even if the transmission frequency of an ultrasonic wave is changed, in other words, the speed display range is not changed. An object of the present invention is to provide an ultrasonic Doppler diagnostic apparatus that does not change.

Another object of the present invention is to provide an ultrasonic Doppler diagnostic apparatus capable of adaptively changing a maximum displayable Doppler shift frequency and a cutoff frequency of a low-pass filter in conjunction with a variably set transmission frequency. Is to do.

[0016]

Means for Solving the Problems [Pulse Doppler Method] In order to achieve the above object, in a desirable configuration, a transmission frequency generation means for generating a transmission frequency f ₀ of a variably set ultrasonic pulse; The transmission repetition frequency f of the ultrasonic pulse is proportional to the transmission frequency f _0.
a repetition frequency generating means for generating _pr, and repeatedly transmitting an ultrasonic pulse having the transmission frequency f ₀ into the living body at the transmission repetition frequency f _pr , and receiving a reflected wave reflected by a moving reflector in the living body. An ultrasonic probe that outputs a received signal by oscillating, a frequency analysis unit that extracts a Doppler shift frequency f _d of the motion reflector from the received signal, and a Doppler image whose speed display range does not depend on the transmission frequency f _0. and means for forming a, characterized in that it comprises a Doppler image forming section for forming the Doppler image based on the Doppler shift frequency f _d of the extracted.

According to the above configuration, when the transmission frequency f ₀ of the ultrasonic pulse is changed, the transmission repetition frequency f _pr of the ultrasonic pulse also changes proportionally, so that the speed display range in the Doppler image is maintained. In other words, if the transmission frequency f ₀ of the ultrasonic pulse is changed, the Doppler shift frequency f _d changes proportionally, but the maximum measurable Doppler shift frequency f _{d max} also changes proportionally in conjunction with it, so that the display the contents will be unchanged regardless of the transmission frequency f _0.

By the way, in the pulse Doppler method, if the transmission repetition frequency _fpr is increased, the maximum measurable depth becomes shallow, and it becomes difficult to measure depending on the depth of the measurement point to be observed. However, if a known method is applied, It is also possible to measure a part deeper than such a maximum depth. For example, in the case where one transmission / reception is defined as one frame, if the reflected wave with respect to the transmission in the n-th frame is received in the (n + 1) -th frame, the restriction on the maximum depth can be overcome. When the transmission repetition frequency f _pr is lowered,
A so-called folding phenomenon is likely to occur. For such a folding phenomenon, a known method for solving the phenomenon can be applied. For example, a technique such as shifting the baseline may be applied.

In a preferred aspect, the repetition frequency generation means includes a frequency divider that divides the transmission frequency f ₀ by 1 / n to generate the transmission repetition frequency f _pr .

In the above configuration, the transmission repetition frequency f
_{The pr} is generated synchronously by dividing the transmission frequency f ₀ by 1 / n. At this time, not only an integer but also a non-integer can be selected as n.

[0021] That is, the transmit repetition frequency f _pr to the transmission frequency f _0, because the associated as _{f pr = f 0 / n ...} (7), proportionally even f ₀ is changed _Fpr changes, the speed display range in the Doppler display can be maintained, and problems such as the conventional waveform fluctuation and hue change can be solved. This means that in the above equation (3), even if f ₀ doubles, f _pr becomes 2
It can be understood from the fact that if the value is doubled, v _max can be maintained.

In a preferred aspect, prior to the frequency analysis, quantization means for quantizing the received signal while using the transmission repetition frequency _fpr as a sampling frequency; and the quantization means and the frequency analysis means. Provided between the means,
A digital filter that performs low-frequency cutoff on the received signal.

In the above configuration, the cut-off frequency of the digital filter provided at the subsequent stage of the quantization means is proportional to the sampling frequency. Under this assumption, when the transmission repetition frequency f _pr changes in conjunction with the transmission frequency f ₀ , the sampling frequency also changes in conjunction therewith, ie,
The cutoff frequency of the digital filter also changes in conjunction with it. In terms of speed, the transmission frequency f ₀
Is changed, the speed at the cutoff point corresponding to the cutoff frequency is maintained.

[Continuous Wave Doppler Method] The above principle can also be applied to the continuous wave Doppler method as it is if the transmission repetition frequency f _pr is replaced by the sampling frequency f _q .

That is, in order to achieve the above object, the present invention provides a transmission frequency generating means for generating a variably set ultrasonic transmission frequency f ₀ , and a transmission frequency f ₀ having a proportional relationship with the generated transmission frequency f ₀ . A sampling frequency generating means for generating a sampling frequency f _q , continuously transmitting an ultrasonic pulse having the transmission frequency f ₀ into a living body, and receiving a reflected wave reflected by a moving reflector in the living body; An ultrasonic probe that outputs a received signal by using the sampling frequency f _q , a quantizing unit that quantizes the received signal at the sampling frequency f _q , and a Doppler shift frequency f _{d of the} motion reflector from the quantized received signal. Frequency analyzing means for extracting, and means for forming a Doppler image whose speed display range does not depend on the transmission frequency f ₀ , wherein the Doppler image forming the Doppler image based on the extracted Doppler shift frequency f _d And an image forming means.

In a preferred aspect of the present invention, the sampling frequency generation means includes a frequency divider that divides the transmission frequency f ₀ by 1 / n to generate the sampling frequency f _q .

In a preferred aspect of the present invention, a digital filter is provided between the quantizing means and the frequency analyzing means and cuts a low band of the received signal.

In both the pulse Doppler method and the continuous wave Doppler method, it is desirable to provide an analog filter that cuts off the low frequency of the received signal before quantization. The cutoff frequency of the analog filter is
The cutoff frequency of the digital filter is set lower than the lowest possible value. That is, prior to quantization, if the signal of a large-amplitude low-speed moving body (mainly a heart wall) or the like is reduced as much as possible by an analog filter, the dynamic range of quantization can be effectively used. If the cut-off frequency of the analog filter is higher than the cut-off frequency of the digital filter, there is a concern that effective blood flow data may be cut depending on the set value of the transmission frequency f ₀ . The analog filter functions within a range that does not hinder the clutter removal.

[0029]

FIG. 1 shows a preferred embodiment of an ultrasonic Doppler diagnostic apparatus according to the present invention. The ultrasonic Doppler diagnostic apparatus shown in FIG. 1 is an apparatus to which a so-called pulse Doppler method is applied.

In FIG. 1, a transmission frequency generator 10 includes
The probe 11 generates a transmission frequency (center frequency) f ₀ of an ultrasonic pulse transmitted into a living body by a probe 11 described later. A frequency setting device 12 is connected to the transmission frequency generator 10, and a user can variably set a desired frequency as the transmission frequency f ₀ using the frequency setting device 12. The signal indicating the generated transmission frequency f ₀ is supplied to the transmitter 14.

The frequency divider 16 divides the generated transmission frequency f ₀ to generate a transmission repetition frequency _fpr . Specifically, the frequency f _{pr is} obtained by dividing f ₀ by n.
Has been generated. An n setting unit 18 is connected to the frequency divider 16, and the user can input and set a desired value as n. This n is not limited to an integer and may be a non-integer. In the present invention, it is sufficient that the transmission repetition frequency f _pr is proportional to the transmission frequency f ₀ , and it is not required that n is an integer. The signal indicating the generated transmission repetition frequency _fpr is supplied to the transmitter 14.

The transmitter 14 is connected to the probe 11 and supplies a transmission signal to the probe 11. The transmission signal is a pulse signal whose center frequency is the transmission frequency f ₀
The repetition period of the transmission signal is set by the transmission repetition frequency _fpr . That is, ultrasonic pulse transmission frequency f ₀ from the probe 11 at the transmission repetition frequency f _pr is repeatedly transmitting in vivo. The echo reflected by the motion reflector in the living body is received by the probe 11 again,
A reception signal is output from this probe.

[0033] The received signal, after a predetermined received signal processing at the receiver 20, for example amplification and made, is sent to the orthogonal detector 22, quadrature detection is performed by the transmission frequency f _0. The received signal after the quadrature detection is sent to a low-pass cutoff analog filter A (hereinafter, filter A) 24 to remove low-frequency components. Here, the filter A is an analog filter, and its cutoff frequency is fixed.

The received signal passing through the filter A is quantized by the quantization circuit 26. That is, quantization is performed in both the time axis direction and the amplitude axis direction. This quantization circuit 26 is constituted by, for example, an A / D converter. The quantization circuit 26 is supplied with the transmission repetition frequency _fpr generated by the frequency divider 16 as a sampling frequency, and the quantization circuit 26 performs sampling at a period based on the sampling frequency. I have. That is, the sampling frequency is proportional to the transmission frequency f _0.

The quantized received signal is then sent to a low-pass cutoff digital filter B (hereinafter, filter B) 28, where the low-pass component is further removed. Filter B28
Is composed of a digital filter circuit, and its cutoff frequency is proportional to the sampling frequency. That is, as the sampling frequency increases, the cutoff frequency of the filter B also increases, while as the sampling frequency decreases, the cutoff frequency of the filter B also decreases. Here, the cutoff frequency of the filter A is
Is set to a value lower than the lowest possible cutoff frequency. That is, in order to remove clutter caused by a slow strong reflector such as a heart wall, only the filter B should be provided, but in order to effectively utilize the dynamic range in the quantization circuit 26, The filter A24 is provided because it is necessary to keep the amplitude of the signal input thereto at a certain level or less. However, if the cutoff frequency of the filter A24 becomes higher than the cutoff frequency of the filter B28, there is no point in setting the cutoff frequency of the filter B adaptively, so that the filter B can take the cutoff frequency of the filter A. It is set lower than the lowest cutoff frequency.

The frequency analyzer 30 is composed of, for example, an FFT circuit or an autocorrelation circuit, and extracts the speed of a blood flow, which is a moving body in a living body, from a received signal that has passed through the filter B. Specifically, the Doppler shift frequency f _d is extracted from the received signal, and finally converted to a velocity value.

DSC (Digital Scan Converter) 3
Reference numeral 2 denotes a circuit for forming a Doppler image, for example, a power spectrum image or a two-dimensional color flow image. These Doppler images are sent to the display unit 34 for image display.

FIG. 2 shows the cutoff characteristics of the filters A and B. As is clear from the above configuration, the cutoff characteristic of the filter B depends on the sampling frequency in the quantization circuit 26, in other words, the transmission repetition frequency _fpr . On the other hand, the cutoff characteristic of the filter A is fixed, and is set to a lower speed side than the lowest cutoff characteristic of the filter B. As shown in FIG. 2, when the transmission frequency f ₀ changes, the frequency distribution (spectrum) of the received signal changes following the transmission frequency f ₀ , that is, the frequency distribution of the clutter also changes. In the embodiment, since the cutoff characteristic of the filter B is changed in conjunction with the change of the transmission frequency f ₀ , only the clutter can be effectively removed.

FIG. 3 shows a power spectrum image displayed on the display unit 34. As described above, the vertical axis corresponds to the blood flow velocity, and the horizontal axis corresponds to the time axis. The brightness at each point corresponds to the power of the blood flow. Conventionally, when the transmission frequency f ₀ is varied in such a power spectrum display, there is a problem that the Doppler shift frequency f _d fluctuates in conjunction therewith, that is, the waveform shown in FIG. 3 is enlarged or reduced. However, according to the apparatus of the present embodiment, the upper and lower frequencies on the vertical axis can be changed in proportion to the change in the transmission frequency f ₀ , in other words, the values of the upper and lower speeds on the vertical axis Can be maintained irrespective of the magnitude of the transmission frequency f ₀ , so that the state can be maintained by preventing waveform fluctuation. That is, according to the present invention,
In such a power spectrum display, with respect to the vertical axis, the display range can be maintained in terms of speed, and can be changed in proportion to the transmission frequency in terms of frequency.

Such an advantage can be similarly obtained in a two-dimensional Doppler image. That is, FIG. 4A shows a two-dimensional Doppler image in which the hue corresponds to the speed.
FIG. 4B shows the correspondence between the hue and the speed, where red is set in the positive direction of the blood flow velocity and blue is set in the negative direction of the blood flow velocity. The magnitude of the positive or negative speed is represented by the color density. Of course, a method of expressing the speed by changing the hue can be applied.

According to the present invention, in such a color bar, even if the transmission frequency f ₀ is varied, the correspondence between the speed and the color does not change at all. _{Even if 0} is changed, the two-dimensional Doppler image appearing in the image can be maintained as it is.

Next, FIG. 5 shows another embodiment of the ultrasonic Doppler diagnostic apparatus according to the present invention. The ultrasonic diagnostic apparatus shown in FIG. 5 is an apparatus to which the continuous wave Doppler method is applied. Note that the same components as those shown in FIG.

In the configuration shown in FIG. 5, the transmission frequency f ₀ generated by the transmission frequency generator 10 is sent to the transmitter 14, and the transmission signal is continuously transmitted from the transmitter 14 to the probe 11. Supplied. As a result, the probe 11 continuously transmits ultrasonic waves into the living body.

On the other hand, the transmission frequency f ₀ is also supplied to the frequency divider 16, which divides the transmission frequency f ₀ by n similarly to the frequency divider 16 shown in FIG. It is generating sampling frequency f _q by. And the quantization circuit 2
Reference _numeral 6 samples the received signal at the generated sampling frequency fq. In such a configuration, to maintain the speed display range in the Doppler image displayed on the display unit, also the cut-off frequency of the filter B28 in proportion changed to the transmission frequency f _0, enables the efficient removal of clutter.

[0045]

As described above, according to the present invention, the display content of the Doppler image can be maintained as it is even if the transmission frequency of the ultrasonic wave is varied. That is, according to the present invention, it is possible to form a Doppler image in which the speed display range does not change even when the transmission frequency of the ultrasonic wave is changed. Further, according to the present invention, the cut-off frequency of the low-band rejection filter is made proportional to the transmission frequency, so that clutter can be efficiently removed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an ultrasonic Doppler diagnostic apparatus according to the present invention.

FIG. 2 is a diagram illustrating cutoff characteristics of a filter A and a filter B.

FIG. 3 is an explanatory diagram showing a power spectrum display.

FIG. 4 is an explanatory diagram showing a two-dimensional Doppler image and a color bar.

FIG. 5 is an overall configuration diagram showing another embodiment of the ultrasonic Doppler diagnostic apparatus according to the present invention.

[Explanation of symbols]

10 transmission frequency generator, 12 frequency setting device, 16
Frequency divider, 18n setting device, 24 low-pass cutoff analog filter A, 26 quantization circuit, 28 low-pass cutoff digital filter B.

Claims (3)

(57) [Claims] 1. An ultrasonic transmission frequency f ₀ that is variably set.
A transmission frequency generation means for generating a, with a proportional relationship between the transmission frequency f ₀ of the generated, the sampling frequency generation means for generating a sampling frequency f _q, the ultrasonic pulse of the transmission frequency f ₀ into the living body continuously transmitting, perform an ultrasonic probe which outputs a received signal receives a reflected wave reflected, the quantization of the received signal at the sampling frequency f _q by movement reflector in vivo Quantization means; frequency analysis means for extracting the Doppler shift frequency f _d of the moving reflector from the quantized received signal; and means for forming a Doppler image whose speed display range does not depend on the transmission frequency f _0. Te, ultrasonic Doppler diagnostic apparatus characterized by comprising: a Doppler image forming section for forming the Doppler image based on the extracted Doppler shift frequency f _d. The apparatus of claim 2 according to claim 1, wherein the sampling frequency generation means, the transmission frequency f ₀ 1
An ultrasonic Doppler diagnostic apparatus comprising a frequency divider that _{divides the} sampling frequency fq by dividing the sampling frequency into / n. 3. A device according to claim 1, provided between the frequency analysis means and the quantization means, ultrasonic waves, characterized in that it comprises a digital filter for low cut-off with respect to the received signal Doppler diagnostic device.